1. Field of the Invention
The present invention generally relates to video or electronic image signal processing, and in particular to techniques for modifying the hue and/or saturation levels of video signals with hue/saturation/brightness directed brightness range changes.
2. Description of Related Art
A wide variety of techniques and systems have been developed for processing electronic or video image signals to add, delete or modify color components of the signals, usually in accordance with operator control. For example, systems have been developed for emphasizing or deemphasizing selected colors or hues within an entire video image signal or within selected portions of the signal. Other systems have been developed for adding color information to an otherwise monochromatic or black and white image.
Conventional systems typically store and manipulate blue, green and red primary color components of an electronic image to allow color modification of either the entire image or portions thereof. To this end, look-up tables are often provided in the memory of the system for converting the primary color components from one brightness or luminance level to another, to thereby modify the resulting hue of the electronic image. An example of the system providing look-up tables for blue, green and red primary colors is set forth in U.S. Pat. No. 4,639,771 to Hattori, et al. Systems which allow for modification of colors within only a portion of an electronic image or video signal include U.S. Pat. No. 4,782,384 to Tucker, et al and U.S. Pat. No. 4,710,800 to Fearing, et al.
Most conventional systems which allow for storage and manipulation of primary color based signals do not operate in real time. Hence, an operator must page through a video signal one frame at a time while varying the colors or hues in each frame. Even if designed to operate without direct operator control, such systems typically process the video signal at a delayed rate. Accordingly, such systems are time consuming and, if operator control is required throughout the process, labor intensive. Thus, such systems are relatively expensive to operate. Furthermore, systems which store and manipulate the individual primary color components of each video display pixel require extensive amounts of computer memory which may be expensive and may further slow the processing time of the video signal. The memory requirements of such a system may be seen by considering the simplified color manipulation system of FIG. 1 which includes input lines for receiving digitized image elements, such as red, green and blue primary color elements, luminance and chromonance elements, or other discrete image elements. Each digitized element is processed by a programmable look-up table which provides an array of values for converting the input elements to obtain desired modified output elements in accordance with operator instructions received through a user interface.
Although the method outlined with reference to FIG. 1 is a simple and viable method for manipulating color image signals, a significant drawback to the method is the amount of memory required within the look-up table. With each of the three input image elements represented by 8 bits, the look-up table may require more than fifty million 8 bit bytes of stored information. The processing time required to access and manipulate the data stored within the look-up table prevents the system from operating effectively in real time. Further, the large amount of memory adds additional costs to a system employing the technique of FIG. 1. To limit the memory requirements, many present systems represent each primary color by only 4-bits, thereby achieving only limited resolution.
As can be appreciated, there is a need to provide a system for allowing color modification of an input video image which uses a limited amount of memory and which is capable of operating in real time.